Hydraulic equalizing system



Jan. 9, 1968 5. B. BARON 3,362,299

HYDRAULIC EQUALIZING SYSTEM Filed July 21, 1966 2 SheetsSheet "Lis INV ENT OR GEO-26E B. B-AIZQN Wmif w gmu ATTORNEYS United States Patent 3,362,299 HYDRAULIC EQUALIZING SYSTEM George B. Baron, Marion, Ohio, assiguor to Marion Power Shovel Company, Inc., Marion, Ohio, 21 corporation of Ohio Filed July 21, 1966, Ser. No. 566,796

6 Claims. (Cl. 91-412) This invention relates in general to any large machine and especially power excavators which are rigidly support ed by four sets of hydraulic jacks and which require movement of the jacks in order to maintain firm support for the machine upon rough ground; and more particularly to a new and novel apparatus for not only leveling the machine, but also for maintaining proper load distribution among the supporting jacks.

It is generally recognized that four supporting jacks and their associated hydraulic systems have the three distinct purposes. (a) leveling to maintain the machine in a level condition, (b) jacking to adjust the elevation of the machine within a small range, and (c) equalizing to obtain the best possible load distribution. The present invention is concerned with the problem of equalization which is a distinct function from either leveling or jacking. In the prior art it has generally been the case on large power excavators to open a valve between two adjacent jacks to equalize the pressures upon them. However, such a valve must-not be left open while the machine is digging because the machine will obviously become much less stable. With such a method of equalization, the resultant of the forces upon the two adjacent jacks is halfway between the jacks on a line'extending between their centers. Thus, the machine is essentially supported by only three points, thereby causing a less stable condition which necessitates that the equalization system be shut down when the machine is digging and its gravity center is moving.

Therefore, if the ground settles under one corner of the machine or if there is an internal or external leak in the hydraulic system, the machine becomes unequalized to some extent thus setting up a twisting action upon the lower supporting frame. This twisting action will cause a certain deflection of the support members and will usually cause a poor distribution of loads around the roller circle upon which the upper supporting frame swings. This is especially so if the upper frame is of appreciable depth and stilfly constructed. This type of system also prohibits digging or other maneuvers from being carried out while the machine is being propelled, due to the reduced stability. When the machine ceases to be propelled and the equalizing valve closes, the machine might not be precisely level due to the inability of the leveling systems to keep pace with the ground contours. Therefore, one or both system may continue to move oil for a short period of time and, due to inaccuracies of the leveling system the pressures on two diametrically opposite jacks may become reduced, thereby shifting most of the weight to the other two diametrically opposite jacks. This means that the machine is essentially balanced upon a straight line and is unequalized. At this point of operation, the operator would normally energize the equalization system which often results in so much settling movement of the machine that one or more of the leveling systems will start moving hydraulic fluid again and the equalization process must be repeated.

Therefore, an object of this invention is to provide large mobile machines having a plurality of rigid groundengaging jacks with an equalization system for the jacks which will equalize continuously without loss of stability to the machine.

Another object of the invention is the provision of an equalization apparatus which is entirely independent unto itself and requires no external source of power.

A further object of this invention is the provision of an equalization apparatus for large mobile machines wherein the apparatus has no moving external seals that may cause leakage.

Yet another object of this invention is the provision of automatic equalization apparatus which is highly sensitive, entirely automatic, and requires very little attention.

A still further object of this invention is the provision of an equalizing apparatus for mobile machines supported by piston operated jacks which is extremely simple in construction, reliable of operation, and inexpensive to manufacture.

Other objects, advantages and capabilities of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings showing only a preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a schematic view of the apparatus of the present invention;

FIGURE 2 is a graphical representation of the weight distribution system of a large mobile machine utilizing four supporting jacks; and

FIGURE 3 is a diagrammatic view of the apparatus of the present invention showing an operable equalizing unit in section view.

Referring to the drawings wherein like reference characters designate corresponding parts throughout the several figures, the four hydraulic jacks are designated by the letters A, B, C and D, and the equalizing unit is designated by the numeral 11. In the preferred embodiment of this invention, the four jacks are arranged preferably in a square pattern or in some other similar geometric pattern as long as the patterns do not depart radically from a square.

The system as shown in FIGURES 1 and 3 includes two leveling and jacking system 12 and 13 in which system 12 interconnects jacks A and C. Leveling and jacking system 13 interconnects jacks B and D. The required leveling of the machine is accomplished by letting the hydraulic fluid out of one jack and pumping it into the diametrically opposite jack. In the particular embodiment illustrated by FIGURE 3, fluid would be pumped from the reservoirs 14, 15 by pump 16 through fluid lines 17, 18 which connect to jacks A and C respectively. In leveling and jacking of the machine, no fluid needs to be sent through the equalizing unit 11 as each of the lines 17 and 18 directly connect with the respective jacks.

In the leveling and jacking system 13 a similar arrangement is found in that fluid is pumped by a suitable pump 19 from reservoirs 21, 22. through fluid lines 23, 24 which connect to jacks B and D respectively. Such a leveling and jacking system does not form a part of the present invention and no further discussion about the system is pertinent except to say that they automatically level the machine and are to be considered insensitive to pressure in the fluid lines.

It is a matter of common knowledge derived from observation that only rarely will a rigid body, when resting upon uneven ground, he supported at four points. Even when this occurs, it is quite rare that each of the four points will bear an equal amount of the load. Accordingly, therefore, it is of utmost importance to provide means whereby the load between the four points is properly distributed. A thorough approach to equalization may be taken by attempting to compute the individual jack loads of a large machine algebraically. The center of gravity of the machine obviously wanders considerably, especially when the machine is operating. Ordinarily, the center of gravity of the machine stays within a circle inscribed in the square of the jacks. Such a circle equations to be solved are:

A+B+ =W 1) by moments about the BD axis:

by moments about the AC axis:

L 7 (b D) Wk However, it should be noted that in the above equations there are four unknowns, and, in order to solve these unknowns simultaneously, there must be four independent equations. The question then resolves as to what should be the fourth equation. In the prior art systems, the fourthequation was determined by opening a valve between two adjacent jacks such as C and D. However, this valve must not be left open while the machine is digging, since it causes the machine to be less stable in operation. By making C and D equal, with their resultant halfway between the jacks at point X, the equalizing valve causes them to act as the equivalent of a single jack being positioned at point X. Therefore, it is obvious that if the center of gravity should move outside of the triangle whose vertices are defined as ABX as shown in FIGURE 2, the machine would begin to tip in an unstable manner since the load on jack A would become negative. Such a system is undesirable, as has been shown before, in that the machine cannot be equalized while operative. In addition, such a system is more complex than the apparatus herein disclosed in that it must be electrically interlocked with the propelling mechanism.

The concept of the present invention is always to equalize across the lightest side of the square whether the machine is operating or not. Therefore, the fourth equation may be one of the following:

Which equation of the above four to use is, of course, determined by the location of the center of gravity. In a situation shown by FIGURE 2, it is obvious that side AD is the light end since the center of gravity is somewhere within the triangle OBC. By taking the moments about the diagonals, it can be seen that C is greater than A, and B is greater than D. Therefore, the system of the present invention must be such that the lower of each of the two jack pressures on each diagonal will be connected to a common line or common fluid chamber.

The schematic diagram of FIGURE 1 shows conventional representation of the present invention utilizing spool valves, however, for clarity of illustration the construction of FIGURE 3 will be explained, since the systems of FIGURES 1 and 3 are identical in operation.

The means for effecting equalization by the concept herein presented is a specific construction for illustrative purposes and includes the equalizing unit in which there is effectively a pair of valve sections 26, 27 within the housings 11a of the unit. Valve 26 generally comprises inlet manifolds 28, 29 which are respectively controlled by poppets 31, 32. Each of the poppets has a configuration such as that of a flattened mushroom in which the underside 33 of each poppet head 34 has circumferential grooves in which there is positioned an O-ring 35 which effects a seal between the poppets and the central valve body 36. The central valve body 36, closed at one end, extends the complete length of the equalizing unit 11, and at the other end accommodates an access hole filler screw 38. Within the central valve body 36 is in an equalizing passage 39 which interconnects each of the valve sections 26, 27. A restrictive orifice 37 is preferably placed in the equalizing passage 39 to prevent undesirably fast fiow of fluid during operation of the machine.

The valve section 27 is constructed similarly to valve section 26 in that a pair of poppet heads 34 effect closure of the respective inlet manifolds 43, 44 against the central valve body 36. By such a construction, four inlet manifolds 28, 29, 43 and 44 are connected common to one another by means of the equalizing passage 39 of the central valve body 36.

Each poppet is mounted in a horizontal position as seen in FIGURE 3 so that the weight of each poppet is carried upon a valve guide rod 40 which comprise plastic sleeves 45, preferably of Teflon. The sleeves are mounted in their proper positions by means of shoulder bolts 46 which screw into the sides of the valves to position the poppets in the proper manner so that they effect a flat leakproof seal against the central valve body 36. A flat poppet seat is preferred because the poppet is not precisely guided upon the guide rod 40 but rather fits in a loose condition for free floating movement. The center of gravity of each poppet is always maintained within the limits of the length of guide rods 40 so that the weight of the poppet will not cause it to become cocked in order that it may bind upon the guide rods. The sleeve is made considerably smaller in diameter than the smooth bore 47 of the poppet stem which encompasses the sleeve. Such a disparity in sizes between the sleeves 45 and from the bore 47 prevents the possibility of the poppet sticking and it allows the free flow of fluid in and out of the blind end of the bore 47. As is seen in FIGURE 3 the poppet stem of each poppet contacts the adjacent poppet at all times at contact surfaces 48. The lengths of the poppet stems are such that when one of the poppets is seated against the central valve body 36 the other poppet is unseated far enough to provide ample opening for fluid flow between respective poppet inlet manifolds and the equalizing passage 39. Inlet manifold 28 is interconnected with leveling system 13 and jack D by means of branch fluid lines 24a and 24b. Likewise, leveling system 13 and jack B are interconnected with inlet manifold 29 by means of branch fluid lines 23a and 23b. Valve 27 interconnects with leveling system 12, jack A and inlet manifold 43 by means of branch fluid lines 17a, 17b, and inlet manifold 44 is interconnected with system 12 and jack C by branch fluid lines 18a, 18b. The poppets of the equalizing unit 11 reciprocate at an extremely low differential pressure and their stems 34a cannot stick or jam upon the sleeves 45 unless the fluid system becomes exceptionally dirty from use.

In operation let it be assumed that the large machine has been leveled by means of systems 12 and 13 and that these two systems are no longer interconnected with the equalizing unit. As shown in FIGURE 3 the positions of the poppets in equalizing unit 11 indicates that the pressure upon jack A is greater than the pressure upon jack C, and likewise, B is greater than D. This is evident because poppets 41 and 32 are in a closed and sealed condition indicating the pressure upon the poppet heads from jack A and B exceeds that from the remaining two jacks. Since poppets 32 and 41 are closed, it is seen that it is a necessity that poppets 31 and 42 remain open. Therefore, there is a free flow of fluid through the equalizing passage 39 with its orifice 37 between jacks C and D. If, during the digging operation, pressure upon jack C becomes greater than that upon jack A, poppet 41 will unseat and become open, since the pressure upon the head of poppet 42 becomes greater than the pressure upon the head of poppet 41. If this occurs, poppet 42 closes and forces poppet 41 open as in a check valve. When poppet 42 closes, jack C is blocked from the equalizing unit and retains its full supply of incompressible fluid thereby interconnecting for equalizing purposes jacks A and D through passage 39 and orifice 37. Under such dynamic conditions such as when the machine might be simultaneously propelling and digging, there may be a large flow of fluid from D to C at the time when the pressure upon jack C becomes greater than the pressure upon jack A. Poppet 42 could remain open after poppet 41 opens, due to this flow. However, such a condition could not last any longer than the time required for the pressure at jack D to be reduced to a pressure equal to that of jack A by means of fluid flow past poppet 41. Therefore, since the condition of equalizing unit 11 indicates that the pressure upon jack C is greater than the pressure upon jack A and that the pressure of jack D is equal to that of jack A, it is obvious that the pressure upon jack C is greater than the pressure upon jack D and the flow of fluid past poppet 42 reverses, thus closing the poppet. Such a transient condition does not represent incipient tipping of the machine since at no time can there be any appreciable flow of fluid from jack C to jack A. It should be obvious that fluid flow on either diagonal through the equalizing unit would cause a total loss of stability since the machine would be essentially suspended upon a three point suspension system with all three points lying upon a straight line. Since the lower frame of a shovel is not absolutely rigid, it has been found that a large open passage between two adjacent jacks, even if these are on the light end, causes undesirably large movements of these jacks while the machine is operating. Therefore, it is necessary to restrict the flow in the equalizing unit, preferably in the equalizing passage 39. The orifice 37 is of such a size that the pressure drop through the equalizing unit is not great enough to be harmful to the machine when it is being propelled over the most uneven terrain expected. However, the pressure drop is great enough to prevent undesirably fast momentary flow during the digging operation. An adjustable needle valve could be used, of course, instead of the fixed orifice.

From the description the advantages of a light end equalizing system as presented herein over a fixed end system should be readily apparent. In the present systern there is virtually no possibility of leakage through poor seals at any time during operation of the machine. In addition, the equalizing unit herein operates equally as well when the machine is in a dynamic condition as when it is in a static condition.

While I have particularly shown and described one particular embodiment of the invention, it is distinctly understood that the invention is not limited thereto, but that modifications may be made within the scope of the invention and such variations as are covered by the scope of the appended claims.

What is claimed is:

1. In combination, a reference table supported by four fluid pressure ground-engaging units, the reference table adapted to apply varying pressure among the individual ground-engaging units, the ground-engaging units each including at least one reciprocable ground-engaging piston adapted to be extended and retracted, means for actuating the unit selectively to effect leveling and positioning of the reference table, the four ground-engaging units generally defining a planar geometrical square having four sides and means for automatically interconnecting two of the ground-engaging units having the lowest piston pressures on the lightest side of the square thereby equalizing the pressures in two adjacent units on the lightest side of the square.

2. A combination according to claim 1, wherein the means for effecting equalizing of the fluid pressure upon the unit comprises an equalizing unit selectively interconnecting to a common fluid chamber the lower of each of the two piston pressures of two groundengaging units located on each diagonal of the square.

3. A combination according to claim 2, wherein each ground-engaging unit has access to the common fluid chamber, valve means controlling the access between the common chamber and the ground-engaging units.

4. A combination according to claim 3, wherein the valve means are responsive to the differentials of fluid pressure among the ground-engaging units to permit transfer of fluid between adjacently disposed groundengaging units.

5. A combination according to claim 4, wherein the valve means include a plurality of individual poppet valves each having a head and a stem, each poppet valve adapted to control the transfer of fluid between the common fluid chamber and one ground-engaging unit, the poppet valves being disposed in pairs so that the individual poppets of each pair act concurrently upon sensing the pressure differential between two ground-engaging units to allow free fluid flow between the ground-engaging units of lesser pressure controlled by a first pair of poppets and the ground-engaging unit of lesser pressure controlled by a second pair of poppets.

6. An equalizing apparatus for maintaining equal pressure upon two adjacently disposed fluid pressure operated ground-engaging units, a structure comprising a normally horizontal reference table having four fluid pressure operated ground-engaging units arranged in a generally geometric square pattern, all units being operatively connected to and supporting the normally horizontal reference table which is adapted to apply varying pressures among the individual ground-engaging units, wherein the equalizing apparatus comprises a housing with valve means disposed within the housing and controlling a plurality of fluid passageways, each passageway being in communication with the interior of the housing, a common fluid chamber within the housing, the fluid passageways each interconnecting with the common fluid chamber and predetermined ones of the passageways interconnecting with the ground-engaging units, the valve means sensing the pressure differential between two diametrically opposite ground-engaging units to allow free fluid flow between the ground-engaging unit of lesser pressure on one of the diagonals of the square and the ground-engaging unit of lesser pressure on the other of the diagonals of the square.

References Cited UNITED STATES PATENTS 2,202,009 5/1940 Knox et al. 280--6 2,229,530 1/1941 South 2806 2,268,017 12/1941 Busick et al. 2806 EDGAR W. GEOGHEGAN, Primary Examiner, 

1. IN COMBINATION, A REFERENCE TABLE SUPPORTED BY FOUR FLUID PRESSURE GROUND-ENGAGING UNITS, THE REFERENCE TABLE ADAPTED TO APPLY VARYING PRESSURE AMONG THE INDIVIDUAL GROUND-ENGAGING UNITS, THE GROUND-ENGAGING UNITS EACH INCLUDING AT LEAST ONE RECIPROCABLE GROUND-ENGAGING PISTON ADAPTED TO BE EXTENDED AND RETRACTED, MEANS FOR ACTUATING THE UNIT SELECTIVELY TO EFFECT LEVELING AND POSITIONING OF THE REFERENCE TABLE, THE FOUR GROUND-ENGAGING UNITS GENERALLY DEFINING A PLANAR GEOMETRICAL SQUARE HAVING FOUR SIDES AND MEANS FOR AUTOMATICALLY INTERCONNECTING TWO OF THE GROUND-ENGAGING UNITS HAVING THE LOWEST PISTON PRESSURES ON THE LIGHTEST SIDE OF THE SQUARE THEREBY EQUALIZING THE PRSSURES IN TWO ADJACENT UNIT ON THE LIGHTEST SIDE OF THE SQUARE. 